Generally, the fabrication of an IC semiconductor device includes performing a lithography process to form a pattern on a specific layer of a semiconductor wafer. The lithography process includes coating photoresist on the semiconductor wafer and exposing and developing the photoresist. Therefore, a photoresist coating apparatus is needed to coat the photoresist on the semiconductor wafer.
With an increase in the integration density of IC semiconductor devices, the spraying amount of photoresist to be coated on a semiconductor wafer must be precisely controlled. However, a conventional photoresist coating apparatus cannot continuously spray a precise amount of photoresist on the semiconductor wafer because of, for example, a variation in the pressure of a pump used for coating the photoresist, a variation in an atmospheric pressure applied to open and close off valves, and the contamination of a nozzle unit.
When a precise amount of photoresist cannot be sprayed on the semiconductor wafer, a nonuniform photoresist layer is uniformly coated on the semiconductor wafer. In this case, exposure and developing processes are performed on the nonuniform photoresist layer, so that a photoresist pattern is not uniformly formed on the semiconductor wafer. The extreme case is that a photoresist coating process and an exposure process need to be performed again or the used semiconductor wafer must be discarded.